Method for Dispensing a Gas

ABSTRACT

A method for dispensing gas within a target temperature range wherein the gas exchanges heat with multiple thermal capacitors to cool the gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. application Ser.No. 13/648,622, filed Oct. 10, 2012, which is a continuation-in-part ofU.S. application Ser. No. 13/542,761, filed Jul. 6, 2012, thespecification and claims of each being incorporated by reference andmade a part of this application.

BACKGROUND

The present invention is particularly suited for dispensing hydrogen tovehicles that use hydrogen as a fuel.

Industry desires to dispense hydrogen gas that has been cooled fromambient temperature down to a temperature within a narrow temperaturerange during the dispensing event. The refrigeration load during thedispensing event is much larger than the average refrigerationrequirement.

In an example dispensing protocol, there is a need to provide hydrogengas at a temperature between −33° C. and −40° C. The hydrogen gas mustbe dispensed within this target temperature range for multiplesequential dispensing events. The dispensing station and method musttherefore be capable of providing sufficient cooling for each of themultiple sequential dispensing events within the target temperaturerange for quantities of gas that will vary both in size, typically 3 to10 kg, and in flow rate, typically 0.25 to 3.6 kg/min.

BRIEF SUMMARY

The present invention relates to a method for dispensing a gas.

There are several aspects of the method as outlined below.

Aspect 1. A method comprising:

-   -   withdrawing a first quantity of the gas from a gas source;    -   cooling the first quantity of gas via heat exchange with a first        thermal capacitor wherein the first thermal capacitor has a        temperature lower than the minimum temperature of a first target        temperature range when the first quantity of gas is initially        cooled by the first thermal capacitor;    -   cooling the first quantity of gas via heat exchange with a        second thermal capacitor wherein the second thermal capacitor        has a temperature lower than the minimum temperature of the        first target temperature range when the first quantity of gas is        initially cooled by the second thermal capacitor, wherein the        first quantity of gas is cooled via heat exchange with the        second thermal capacitor after being cooled via heat exchange        with the first thermal capacitor;    -   heating or cooling the first quantity of gas via heat exchange        with a third thermal capacitor wherein the third thermal        capacitor has a temperature within the first target temperature        range, wherein the first quantity of gas exchanges heat with the        third thermal capacitor after being cooled via heat exchange        with the second thermal capacitor; and    -   introducing the first quantity of gas from the third thermal        capacitor into a first receiving vessel, the first quantity of        gas thereby having a dispensing temperature within the first        target temperature range.

Aspect 2. The method of aspect 1 wherein the first quantity of gas isheated via heat exchange with the third thermal capacitor.

Aspect 3. The method of aspect 1 or aspect 2 further comprising:

-   -   withdrawing a second quantity of the gas from the gas source;    -   cooling the second quantity of gas via heat exchange with the        first thermal capacitor;    -   cooling the second quantity of gas via heat exchange with the        second thermal capacitor, wherein the second quantity of gas is        cooled via heat exchange with the second thermal capacitor after        being cooled via heat exchange with the first thermal capacitor;    -   heating or cooling the second quantity of gas via heat exchange        with the third thermal capacitor wherein the third thermal        capacitor has a temperature within the first target temperature        range, wherein the second quantity of gas exchanges heat with        the third thermal capacitor after being cooled via heat exchange        with the second thermal capacitor; and    -   introducing the second quantity of gas from the third thermal        capacitor into a second receiving vessel, the second quantity of        gas thereby having a dispensing temperature within the first        target temperature range.

Aspect 4. The method of any one of aspects 1 to 3 further comprising:

-   -   cooling the first thermal capacitor, the second thermal        capacitor, and the third thermal capacitor via heat exchange        with a refrigerant, wherein the refrigerant is cycled in a        refrigeration cycle.

Aspect 5. The method of aspect 4 wherein the flow rate of therefrigerant to each of the first thermal capacitor, the second thermalcapacitor, and the third thermal capacitor is independently controlled.

Aspect 6. The method of any one of aspects 1 to 3 further comprising:

-   -   cooling the first thermal capacitor and the second thermal        capacitor via heat exchange with a refrigerant, wherein the        refrigerant is cycled in a refrigeration cycle; and    -   cooling the third thermal capacitor via heat exchange with a        second refrigerant, wherein the second refrigerant is cycled in        a second refrigeration cycle.

Aspect 7. The method of any one of aspects 4 to 6 wherein therefrigerant is selected from the group consisting of R22, R404A, andR507.

Aspect 8. The method of aspect 6 wherein the second refrigerant isselected from the group consisting of R22, R404A, and R507.

Aspect 9. The method of any one of aspects 1 to 8 further comprising:

-   -   withdrawing a third quantity of the gas from the gas source;    -   cooling the third quantity of gas via heat exchange with the        first thermal capacitor;    -   cooling the third quantity of gas via heat exchange with the        second thermal capacitor, wherein the third quantity of gas is        cooled via heat exchange with the second thermal capacitor after        being cooled via heat exchange with the first thermal capacitor;    -   heating or cooling the third quantity of gas via heat exchange        with a fourth thermal capacitor wherein the fourth thermal        capacitor has a temperature within a second target temperature        range, wherein the second target temperature range is different        than the first target temperature range, and wherein the third        quantity of gas exchanges heat with the fourth thermal capacitor        after being cooled via heat exchange with the second thermal        capacitor; and    -   introducing the third quantity of gas from the fourth thermal        capacitor into a third receiving vessel, the third quantity of        gas thereby having a dispensing temperature within the second        target temperature range.

Aspect 10. The method of aspect 9 further comprising:

-   -   measuring an ambient temperature representative of conditions        surrounding a fourth receiving vessel;    -   withdrawing a fourth quantity of the gas from the gas source;    -   cooling the fourth quantity of gas via heat exchange with the        first thermal capacitor;    -   cooling the fourth quantity of gas via heat exchange with the        second thermal capacitor, wherein the fourth quantity of gas is        cooled via heat exchange with the second thermal capacitor after        being cooled via heat exchange with the first thermal capacitor;    -   heating or cooling the fourth quantity of gas via heat exchange        with one of the third thermal capacitor and the fourth thermal        capacitor, the third thermal capacitor having its temperature        within the first temperature range, the fourth thermal capacitor        having its temperature within the second temperature range, the        selection of heating or cooling the fourth quantity of gas via        heat exchange with the third thermal capacitor or the fourth        thermal capacitor dependent upon the measured ambient        temperature surrounding the fourth receiving vessel; and    -   introducing the fourth quantity of gas from the third thermal        capacitor or from the fourth thermal capacitor into the fourth        receiving vessel, the fourth quantity of gas thereby having a        dispensing temperature within the first target temperature range        when the fourth quantity of gas exchanges heat with the third        thermal capacitor or having a dispensing temperature within the        second target temperature range when the fourth quantity of gas        exchanges heat with the fourth thermal capacitor.

Aspect 11. The method of any one of aspects 1 to 10 wherein at least oneof the first thermal capacitor, the second thermal capacitor, and thethird thermal capacitor comprises a metal.

Aspect 12. The method of aspect 11 wherein the metal is aluminum.

Aspect 13. The method of any one of aspects 1 to 9 wherein at least oneof the first thermal capacitor, the second thermal capacitor, and thethird thermal capacitor comprises a liquid.

Aspect 14. The method of aspect 13 wherein the liquid is a liquidhydrocarbon.

Aspect 15. The method of aspect 14 wherein the liquid hydrocarbon is aC10-C13 iso-alkane.

Aspect 16. The method of any one of aspects 1 to 15 further comprising:

-   -   withdrawing a fifth quantity of the gas from the gas source; and    -   introducing the fifth quantity of gas from the gas source into a        fifth receiving vessel without cooling the fifth quantity of gas        between withdrawing the fifth quantity of gas from the gas        source and introducing the fifth quantity of gas into the fifth        receiving vessel.

Aspect 17. The method of any one of the preceding aspects furthercomprising:

-   -   measuring an ambient temperature representative of conditions        surrounding the first receiving vessel prior to withdrawing the        first quantity of gas from the gas source; and    -   setting the first target temperature range dependent upon the        measured ambient temperature prior to withdrawing the first        quantity of gas from the gas source.

BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

The sole FIGURE is a schematic of a system suitable for carrying out themethod.

DETAILED DESCRIPTION

The articles “a” and “an” as used herein mean one or more when appliedto any feature in embodiments of the present invention described in thespecification and claims. The use of “a” and “an” does not limit themeaning to a single feature unless such a limit is specifically stated.The article “the” preceding singular or plural nouns or noun phrasesdenotes a particular specified feature or particular specified featuresand may have a singular or plural connotation depending upon the contextin which it is used. The adjective “any” means one, some, or allindiscriminately of whatever quantity. The term “and/or” placed betweena first entity and a second entity means one of (1) the first entity,(2) the second entity, and (3) the first entity and the second entity.The term “and/or” placed between the last two entities of a list of 3 ormore entities means at least one of the entities in the list.

The phrase “at least a portion” means “a portion or all.” The at least aportion of a stream may have the same composition as the stream fromwhich it is derived. The at least a portion of a stream may includespecific components of the stream from which it is derived.

As used herein, “first,” “second,” “third,” etc. are used to distinguishfrom among a plurality of steps and/or features, and is not indicativeof the relative position in time and/or space.

Compressed natural gas (CNG) and hydrogen are the typical componentsdispensed from storage systems, which are usually installed outdoors andare therefore subjected to wide ranges of ambient temperatures. Ambienttemperatures are well above the critical temperature of hydrogen (−240°C. (−400° F.)) and methane (−83° C. (−117° F.)), so that thesecomponents typically are stored and dispensed as supercritical fluidsrather than gases according to strict thermodynamic definitions.However, the terms “gas” and “compressed gas” are usually used in theart as generic terms for both gases and supercritical fluids. In thepresent disclosure, the terms “gas” and “compressed gas” may be usedinterchangeably and are meant to include elements and compounds in boththermodynamic states of gas and supercritical fluid. The generic term“fluid” as used herein includes both thermodynamic states of gas andsupercritical fluid.

A gas dispensing system is defined as a pressurized gas storage andsupply system for providing pressurized gas to a portable receiving tankor vessel. The gas dispensing system includes a connector to couple withthe receiving vessel for gas transfer and an appropriate safetyinterlock system to ensure safe operation during the filling step. Thereceiving tank or vessel typically is part of a vehicle such as a car,truck, bus, or forklift.

The present invention relates to a method for dispensing a gas, forexample H₂, at a temperature within one or more target temperatureranges. Target temperature ranges may be preset by the device orselected by a user or operator. The target temperature ranges may bedependent on a measured ambient temperature. The target temperatureranges may be dependent on a measured temperature of the receivingvessel and/or gas in the receiving vessel. Each target temperature rangehas its prescribed minimum temperature and maximum temperature.

The method will be described with reference to the figure illustrating asuitable apparatus for carrying out the method.

The apparatus comprises a gas source 7, at least three thermalcapacitors 101, 103, and 107, a compressor 157, a heat exchanger(condenser) 117, a controller 119, temperature measurement devices 29,31, and 35, and various conduits and valves. The apparatus may compriseone or more optional thermal capacitors 105 and 207 with correspondingtemperature measurement devices 33 and 37.

The method comprises withdrawing a first quantity of gas from gas source7. The gas source may be one or more tanks or vessels, a pipeline, orany other known source for the gas. The first quantity of gas may be anamount sufficient to refill a vehicle fuel tank, for example 3 kg to 10kg.

The first quantity of gas is cooled via heat exchange with first thermalcapacitor 101. Upon initial cooling of the first quantity of gas, thefirst thermal capacitor 101 has a temperature that is lower than theminimum temperature of a first target temperature range. For example, ifthe first target temperature range is −33° C. to −40° C., thetemperature of the first thermal capacitor 101 is less than −40° C. Thetemperature of the first thermal capacitor 101 may be as cold as −60° C.

As used herein, a thermal capacitor is any thermal storage elementcapable of releasing heat to a refrigerant and/or the gas, and absorbingheat from the refrigerant and/or the gas. A thermal capacitor may have athermal mass greater than 40 kJ/K. The thermal mass is the mass of anobject multiplied by the specific heat capacity of the object. A thermalcapacitor may comprise a metal. The metal may be aluminum. A thermalcapacitor may comprise a liquid. The liquid may be a liquid hydrocarbon.The liquid hydrocarbon may be a C10 to C13 iso-alkane, for exampleTherminol® D12 heat transfer fluid. A thermal capacitor may comprise aphase change material. The phase change material may be a eutecticcomprising Sb, Te, and Ge (cf. Phase Change Materials, Science andApplications, Simone Raoux and Matthias Wuttig, Editors, SpringerScience+Business Media, New York, 2009.

Thermal capacitors are preferably insulated to prevent heating of thethermal capacitors by the surrounding ambient air.

After being cooled via heat exchange with the first thermal capacitor,the first quantity of gas is cooled via heat exchange with secondthermal capacitor 103. Upon initial cooling of the first quantity ofgas, the second thermal capacitor 103 has a temperature that is lowerthan the minimum temperature of the first target temperature range.

After being cooled via heat exchange with the second thermal capacitor,the first quantity of gas may be heated or cooled via heat exchange witha third thermal capacitor 107. The third thermal capacitor has atemperature within the first target temperature range. If thetemperature of the first quantity of gas is less than the minimumtemperature of the first target temperature range after exchanging heatwith previous thermal capacitors, the third thermal capacitor 107 willheat the first quantity of gas to a temperature within the first targettemperature range. If the temperature of the first quantity of gas isgreater than the maximum temperature of the first target temperaturerange after exchanging heat with previous thermal capacitors, the thirdthermal capacitor 107 will cool the first quantity of gas to atemperature within the first target temperature range.

After the temperature of the first quantity of gas has been broughtwithin first target temperature range via heat exchange with the thirdthermal capacitor, the first quantity of gas, having a dispensingtemperature within the first target temperature range, is introducedinto a first receiving vessel (not shown) via conduit 137 and adispensing connector (not shown). The first receiving vessel may be partof a vehicle such as a car, truck, bus, or forklift. The dispensingconnector may be any suitable dispensing connector for dispensing thegas to a receiving vessel. Dispensing connectors are known in the art.

The gas flow rate may be controlled to provide a specified mass flowrate or a pressure ramp rate.

As shown in the figure, the first quantity of gas may be cooled byadditional thermal capacitors 105 between cooling in the second thermalcapacitor 103 and heating or cooling in the third thermal capacitor 107.

The thermal masses of the thermal capacitors may be the same ordifferent. The first thermal capacitors in the series may each have thesame thermal mass while the final thermal capacitor has a differentthermal mass. The first thermal capacitor in the series may have athermal mass different from the remaining thermal capacitors in theseries.

The advantage of using multiple thermal capacitors is that the thermalcapacitors that the gas passes through first may be cooled well belowthe target temperature range. The gas is brought within the targettemperature range via heat exchange with the final thermal capacitor.Properly designed, there is then no risk of delivering the gas at atemperature below the minimum temperature of the target temperaturerange. By cooling the first thermal capacitors below the minimumtemperature of the target temperature range allows the compressor to runlonger once turned on.

After the first quantity of gas has been dispensed to the firstreceiving vessel, a second quantity of gas having a temperature withinthe first target temperature range may be dispensed to a secondreceiving vessel.

The method may further comprise withdrawing a second quantity of gasfrom gas source 7. The second quantity of gas may be an amountsufficient to refill a vehicle fuel tank, for example 3 kg to 10 kg.

The second quantity of gas is cooled via heat exchange with firstthermal capacitor 101. The second quantity of gas is subsequently cooledvia heat exchange with second thermal capacitor 103.

After being cooled via heat exchange with the second thermal capacitor,the second quantity of gas may be heated or cooled via heat exchangewith the third thermal capacitor 107. The third thermal capacitor has atemperature within the first target temperature range. If thetemperature of the second quantity of gas is less than the minimumtemperature of the first target temperature range after exchanging heatwith previous thermal capacitors, the third thermal capacitor 107 willheat the second quantity of gas to a temperature within the first targettemperature range. If the temperature of the second quantity of gas isgreater than the maximum temperature of the first target temperaturerange after exchanging heat with previous thermal capacitors, the thirdthermal capacitor 107 will cool the second quantity of gas to atemperature within the first target temperature range.

After the temperature of the second quantity of gas has been broughtwithin the first target temperature range via heat exchange with thethird thermal capacitor, the second quantity of gas, having a dispensingtemperature within the first target temperature range, is introducedinto a second receiving vessel (not shown) via conduit 137 and adispensing connector (not shown). The second receiving vessel may bepart of a vehicle such as a car, truck, bus, or forklift.

The second quantity of gas may be cooled by additional thermalcapacitors 105 between cooling in the second thermal capacitor 103 andheating or cooling in the third thermal capacitor 107.

Setting of the minimum and maximum values for the first targettemperature range may be dependent upon a measured ambient temperature.The method may comprise measuring an ambient temperature representativeof conditions surrounding any receiving vessels prior to filling. Theambient temperature may be measured by any suitable temperature sensor,shown schematically in the figure as temperature sensor 57. Presumably,the temperature of any residual gas in receiving vessels prior tofilling will be at or near ambient temperature. The temperature sensor57 for determining the ambient temperature should generally not be indirect sunlight. Setting of the minimum and maximum values of the firsttarget temperature range may be dependent upon any measured temperaturein the receiving vessel prior to fill, the measured temperature as maybe available from a communication fill. This may be suitable todetermine if the vehicle, for example on a cold day, just arrived forrefueling from a warm garage, thus having a receiving vessel at atemperature higher than ambient temperature.

The reason for adjusting the minimum and maximum values for the firsttarget temperature range is that the degree of cooling necessary toprevent overheating of the receiving vessel may depend on the ambienttemperature. On cold days, less cooling of the gas is required.Furthermore, by maintaining the thermal capacitors at highertemperatures on cold days saves on energy required for cooling thethermal capacitors.

It may be desirable to have the option to dispense different batches ofgas within different target temperature ranges, for example, dependingupon the ambient temperature and/or temperature of the receiving vessel.

A third quantity of gas may be dispensed to a third receiving vesselwherein the third quantity of gas is dispensed at a dispensingtemperature within a second target temperature range wherein the secondtarget temperature range is different than the first target temperaturerange. The second target temperature range may be preset by the deviceor selected by a user or operator. The second target temperature rangehas a minimum temperature and a maximum temperature.

For example, the first target temperature range may be −40° C. to −33°C. and the second target temperature range may be −20° C. to +3° C. Theuser or operator may want the option to choose whether to dispense thegas within the first temperature range or the second temperature range.The first temperature range may be selected, for example, if the ambienttemperature is greater than 15° C. and/or the temperature measured inthe receiving tank is greater than 15° C., and the second temperaturerange may be selected if the ambient temperature is less than 15° C.

In case, it is desired to dispense the gas within the second temperaturerange, the method may further comprise withdrawing a third quantity ofgas from gas source 7. The third quantity of gas may be an amountsufficient to refill a vehicle fuel tank, for example 3 kg to 10 kg.

The third quantity of gas is cooled via heat exchange with first thermalcapacitor 101. The third quantity of gas is subsequently cooled via heatexchange with second thermal capacitor 103.

After being cooled via heat exchange with the second thermal capacitor,the third quantity of gas may be heated or cooled via heat exchange witha fourth thermal capacitor 207. The fourth thermal capacitor has atemperature within the second target temperature range. If thetemperature of the third quantity of gas is less than the minimumtemperature of the second target temperature range after exchanging heatwith previous thermal capacitors, the fourth thermal capacitor 207 willheat the third quantity of gas to a temperature within the second targettemperature range. If the temperature of the third quantity of gas isgreater than the maximum temperature of the second target temperaturerange after exchanging heat with previous thermal capacitors, the fourththermal capacitor 207 will cool the third quantity of gas to atemperature within the second target temperature range.

After the temperature of the third quantity of gas has been broughtwithin second target temperature range via heat exchange with the fourththermal capacitor, the third quantity of gas, having a dispensingtemperature within the second target temperature range, is introducedinto a third receiving vessel (not shown) via conduit 237 and adispensing connector (not shown). The third receiving vessel may be partof a vehicle such as a car, truck, bus, or forklift.

The third quantity of gas may be cooled by additional thermal capacitors105 between cooling in the second thermal capacitor 103 and heating orcooling in the fourth thermal capacitor 207.

Thermal capacitors 101, 103, 105 (if present), 107 and 207 (if present)are cooled in order to provide cooling of the gas. The thermalcapacitors may be cooled by heat exchange with a refrigerant. Therefrigerant may be any suitable refrigerant known in the art, forexample, R508A. The refrigerant is cycled in a refrigeration cycle. Asshown in the figure, the refrigerant is compressed in compressor 157,cooled in heat exchanger (condenser) 117 and expanded through expansionvalves 39, 41, 43 (if present), 45 and 245 (if present). The compressorand heat exchanger may be part of a chiller unit such as a TrentonRefrigeration model T150V6-HT3AB. The refrigerant expanded through valve39 cools thermal capacitor 101. The refrigerant expanded through valve41 cools thermal capacitor 103. The refrigerant expanded through valve43 cools thermal capacitor 105. The refrigerant expanded through valve45 cools thermal capacitor 107. The refrigerant expanded through valve245 cools thermal capacitor 207.

The thermal capacitors may be cooled by the refrigerant while the gas isbeing cooled by the thermal capacitors. The thermal capacitors may becooled by the refrigerant at a time when no gas is being cooled by thethermal capacitors.

The flow rate of the refrigerant to each of the thermal capacitors maybe independently controlled as shown in the figure by valves 121, 123,125, 127, and 129.

The temperature of each of the thermal capacitors may be individuallycontrolled by controlling the flow rate of refrigerant to eachrespective thermal capacitor.

Temperature measurement devices 29, 31, 33, 35, and 37 measure thetemperature of their respective thermal capacitors. Controller 119receives signals from the temperature measurement devices and controlsthe flow rate of refrigerant through valves 121, 123, 125, 127, and 129in order to maintain the desired temperatures for the thermalcapacitors.

In order to prevent heat conduction between each of the thermalcapacitors, any connecting pipes, tubes and the like may constructedfrom materials having low thermal conductivity. For example, stainlesssteel may be used rather than copper or brass or other materials thatare commonly used for refrigeration units.

Since the article “a” means “one or more,” a second refrigerant, asecond compressor, and a second heat exchanger (condenser) may be usedin a second refrigeration cycle. Some of the thermal capacitors may becooled by a first refrigerant cycled in a first refrigeration cycle andsome other thermal capacitors may be cooled by a second refrigerant in asecond refrigeration cycle. The first refrigerant and the secondrefrigerant may be the same or different.

The advantage of using multiple refrigeration cycles is that thedispensing station capacity is increased while allowing each of theindividual compressors to remain on for longer periods of time onceturned on, thereby increasing the life of each compressor.

In some instances, a receiving vessel in a sequence of receiving vesselsto receive the gas may not be capable of receiving cold gas. For thiscase an optional bypass line 301 is provided to bypass all the thermalcapacitors. Consequently, the method may further comprise withdrawing afourth quantity of gas from the gas source 7, and introducing the fourthquantity of gas from the gas source into a fourth receiving vesselwithout cooling the fourth quantity of gas between withdrawing thefourth quantity of gas from the gas source and introducing the fourthquantity of gas into the fourth receiving vessel.

Example (Comparative Case)

A single large aluminum block used to cool down hydrogen from 35° C. to−40° C. at the start of a 5 kg fill, and warming to the point where thehydrogen gas exits the aluminum block at −33° C. at the end of the fillwould need to weigh about 780 kgs. The aluminum block would not be ableto be used again for cooling the hydrogen gas down to −33° C. until thealuminum block is completely recooled after the fill.

Example (Multiple Thermal Capacitors)

This example contemplates a system with four thermal capacitors inseries for cooling hydrogen gas. The target temperature range fordispensing the hydrogen gas is −37° C. to −40° C. in this example.

Each of the four thermal capacitors are made from aluminum and have amass of 200 kg corresponding to a thermal mass of about 182 kJ/K. Forthis example, the thermal capacitors are assumed to be perfectlyinsulated.

Initially the first thermal capacitor, the second thermal capacitor, andthe third thermal capacitor are at −50° C. and the final thermalcapacitor is −37° C.

A flow rate of hydrogen totaling 5 kg is passed through each of thethermal capacitors. The initial gas temperature from the gas source is35° C. The initial portion of hydrogen that exits from the first thermalcapacitor exits at a temperature of about −43° C. and the last portionexits at a temperature of about −13° C. The first thermal capacitorwarms from −50° C. to −17° C. as the first quantity of hydrogen ispassed through the first thermal capacitor.

Hydrogen entering the second thermal capacitor will exit at temperaturesfrom −49° C. to −32° C. as the second thermal capacitor warms from −50°C. to −46° C. Hydrogen entering the third thermal capacitor will exit attemperatures from −45° C. to −39° C. as the third thermal capacitorwarms from −45° C. to −44° C. Hydrogen entering the final thermalcapacitor will exit at a constant −37° C. as the final thermal capacitorcools from −37° C. to −38° C.

When it comes time to fill a second receiving vessel, if therefrigeration plant is running, and has sufficient time between fills,all of the thermal capacitors will be cooled to their normal conditions(e.g. =50° C. for the first, second, and third thermal capacitor, and−38° C. for the final thermal capacitor).

If the refrigeration unit provides no cooling to the thermal capacitorsafter filling the first receiving vessel and before filling the secondreceiving vessel, the example assumes that the thermal capacitorsmaintain their temperature at the end of filling the first receivingvessel (−17° C. for the first thermal capacitor, −46° C. for the secondthermal capacitor, −44° C. for the third thermal capacitor, and −38° C.for the final thermal capacitor).

A second batch of hydrogen totaling 5 kg is passed through each of thethermal capacitors. The initial gas temperature of the second batch ofgas from the gas source is 35° C. The initial portion of hydrogen thatexits from the first thermal capacitor exits at a temperature of about−13° C. and the last portion exits at a temperature of about +6° C. Thefirst thermal capacitor warms from −17° C. to +2° C. as the secondquantity of hydrogen is passed through the first thermal capacitor.

Hydrogen entering the second thermal capacitor will exit at temperaturesfrom −44° C. to −22° C. as the second thermal capacitor warms from −46°C. to −39° C. Hydrogen entering the third thermal capacitor will exit attemperatures from −44° C. to −34° C. as the third thermal capacitorwarms from −44° C. to −43° C. Hydrogen entering the final thermalcapacitor will exit at a constant −37° C. as the final thermal capacitorstays at a constant −38° C.

In this example, the system will continue to keep the hydrogen withinthe target temperature range for two more fills without needing to turnon the refrigeration unit. Once the relatively small refrigeration unit(10 kW for example) turns on, it can run for up to 15 minutes pervehicle filled, an hour of continuous running if four vehicles arefilled, allowing the refrigeration unit to be sized to balance theaverage thermal demand, not just the peak refrigeration demand. Theexiting gas temperature stays at a constant temperature, and is notaffected by changes in flow rates.

We claim:
 1. A method for dispensing gas, the method comprising:dispensing a gas from a gas source at an initial temperature into areceiving vessel at a dispensing temperature, the dispensing temperatebeing within a first target temperature range and being lower than theinitial temperature; cooling the gas from the initial temperature to thedispensing temperature during the dispensing step via heat exchange witha plurality of thermal capacitors arranged in series; circulating arefrigerant to each of the plurality of thermal capacitors using arefrigeration unit; and performing the circulating step for each of theplurality of thermal capacitors as a function of a measured temperatureof each of the plurality of thermal capacitors and independently ofwhether the cooling step is being performed.
 2. The method of claim 1,further comprising: repeating the dispensing step without performing thecirculating step, wherein the dispensing step comprises dispensing atleast 3 kg of the gas.
 3. The method of claim 1, further comprising:providing each of the plurality of thermal capacitors with a sufficientthermal mass to enable a dispensing step in which at least 5 kg of gasis dispensed without performing the circulating step.
 4. The method ofclaim 1, further comprising: performing at least a portion of thecirculating step when the dispensing step is not being performed.
 5. Themethod of claim 1, wherein the cooling step comprises cooling the gasvia heat exchange with at least two of the plurality of thermalcapacitors and heating the gas via heat exchange with a last of theplurality of thermal capacitors.
 6. A method for dispensing a gas, themethod comprising: withdrawing a first quantity of the gas from a gassource, the first quantity of gas having an initial temperature; coolingthe first quantity of gas via heat exchange with a first thermalcapacitor wherein the first thermal capacitor has a temperature lowerthan the minimum temperature of a first target temperature range whenthe first quantity of gas is initially cooled by the first thermalcapacitor; cooling the first quantity of gas via heat exchange with asecond thermal capacitor wherein the second thermal capacitor has atemperature lower than the minimum temperature of the first targettemperature range when the first quantity of gas is initially cooled bythe second thermal capacitor, wherein the first quantity of gas iscooled via heat exchange with the second thermal capacitor after beingcooled via heat exchange with the first thermal capacitor; heating thefirst quantity of gas via heat exchange with a third thermal capacitorwherein the third thermal capacitor has a temperature within the firsttarget temperature range, wherein the first quantity of gas exchangesheat with the third thermal capacitor after being cooled via heatexchange with the second thermal capacitor; and introducing the firstquantity of gas from the third thermal capacitor into a first receivingvessel, the first quantity of gas thereby having a dispensingtemperature within the first target temperature range, wherein thedispensing temperature is less than the initial temperature.
 7. Themethod of claim 6 further comprising: withdrawing a second quantity ofthe gas from the gas source; cooling the second quantity of gas via heatexchange with the first thermal capacitor; cooling the second quantityof gas via heat exchange with the second thermal capacitor, wherein thesecond quantity of gas is cooled via heat exchange with the secondthermal capacitor after being cooled via heat exchange with the firstthermal capacitor; heating or cooling the second quantity of gas viaheat exchange with the third thermal capacitor wherein the third thermalcapacitor has a temperature within the first target temperature range,wherein the second quantity of gas exchanges heat with the third thermalcapacitor after being cooled via heat exchange with the second thermalcapacitor; and introducing the second quantity of gas from the thirdthermal capacitor into a second receiving vessel, the second quantity ofgas thereby having a dispensing temperature within the first targettemperature range.
 8. The method of claim 6 further comprising: coolingthe first thermal capacitor, the second thermal capacitor, and the thirdthermal capacitor via heat exchange with a refrigerant, wherein therefrigerant is cycled in a refrigeration cycle.
 9. The method of claim 8wherein the flow rate of the refrigerant to each of the first thermalcapacitor, the second thermal capacitor, and the third thermal capacitoris independently controlled.
 10. The method of claim 6 furthercomprising: cooling the first thermal capacitor and the second thermalcapacitor via heat exchange with a refrigerant, wherein the refrigerantis cycled in a refrigeration cycle; and cooling the third thermalcapacitor via heat exchange with a second refrigerant, wherein thesecond refrigerant is cycled in a second refrigeration cycle.
 11. Themethod of claim 6 further comprising: withdrawing a third quantity ofthe gas from the gas source; cooling the third quantity of gas via heatexchange with the first thermal capacitor; cooling the third quantity ofgas via heat exchange with the second thermal capacitor, wherein thethird quantity of gas is cooled via heat exchange with the secondthermal capacitor after being cooled via heat exchange with the firstthermal capacitor; heating or cooling the third quantity of gas via heatexchange with a fourth thermal capacitor wherein the fourth thermalcapacitor has a temperature within a second target temperature range,wherein the second target temperature range is different than the firsttarget temperature range, and wherein the third quantity of gasexchanges heat with the fourth thermal capacitor after being cooled viaheat exchange with the second thermal capacitor; and introducing thethird quantity of gas from the fourth thermal capacitor into a thirdreceiving vessel, the third quantity of gas thereby having a dispensingtemperature within the second target temperature range.
 12. The methodof claim 11 further comprising: measuring an ambient temperaturerepresentative of conditions surrounding a fourth receiving vessel;withdrawing a fourth quantity of the gas from the gas source; coolingthe fourth quantity of gas via heat exchange with the first thermalcapacitor; cooling the fourth quantity of gas via heat exchange with thesecond thermal capacitor, wherein the fourth quantity of gas is cooledvia heat exchange with the second thermal capacitor after being cooledvia heat exchange with the first thermal capacitor; heating or coolingthe fourth quantity of gas via heat exchange with one of the thirdthermal capacitor and the fourth thermal capacitor, the third thermalcapacitor having its temperature within the first temperature range, thefourth thermal capacitor having its temperature within the secondtemperature range, the selection of heating or cooling the fourthquantity of gas via heat exchange with the third thermal capacitor orthe fourth thermal capacitor dependent upon the measured ambienttemperature surrounding the fourth receiving vessel; and introducing thefourth quantity of gas from the third thermal capacitor or from thefourth thermal capacitor into the fourth receiving vessel, the fourthquantity of gas thereby having a dispensing temperature within the firsttarget temperature range when the fourth quantity of gas exchanges heatwith the third thermal capacitor or having a dispensing temperaturewithin the second target temperature range when the fourth quantity ofgas exchanges heat with the fourth thermal capacitor.
 13. The method ofclaim 6 wherein at least one of the first thermal capacitor, the secondthermal capacitor, and the third thermal capacitor comprises a metal.14. The method of claim 13 wherein the metal is aluminum.
 15. The methodof claim 6 wherein at least one of the first thermal capacitor, thesecond thermal capacitor, and the third thermal capacitor comprises aliquid.
 16. The method of claim 15 wherein the liquid is a liquidhydrocarbon.
 17. The method of claim 16 wherein the liquid hydrocarbonis a C10 to C13 iso-alkane.
 18. The method of claim 6 furthercomprising: withdrawing a fifth quantity of the gas from the gas source;and introducing the fifth quantity of gas from the gas source into afifth receiving vessel without cooling the fifth quantity of gas betweenwithdrawing the fifth quantity of gas from the gas source andintroducing the fifth quantity of gas into the fifth receiving vessel.19. The method of claim 6 further comprising: measuring an ambienttemperature representative of conditions surrounding the first receivingvessel prior to withdrawing the first quantity of gas from the gassource; and setting the first target temperature range dependent uponthe measured ambient temperature prior to withdrawing the first quantityof gas from the gas source.